FIG. 1 illustrates a ground fault detection circuit (GFD) that has been used in most of the battery management systems.
The ground fault detection circuit determines an isolation breakdown of a battery by forming a current path connected to a positive terminal of a battery, a ground, and a negative terminal thereof and measuring voltage applied to a resistor R.
That is, the ground fault detection circuit alternately opens and closes a switch S (+) and S (−) using voltage V applied to a high-voltage battery to measure the voltage applied to the resistor R and since an insulation resistance value RISO is reduced when a voltage of a predetermined level or more is applied to the resistor, determines that the isolation breakdown occurs.
Therefore, the ground fault detection circuit has a problem in that voltage applied to an operational amplifier may be changed according to a change in the voltage V of the battery even in the case of the same insulation resistance value RISO. Further, according to the circuit illustrated in FIG. 1, it is assumed that insulation resistor RISO− between the negative terminal of the battery and the ground of the vehicle has an infinite resistance value at the time of measuring insulation resistor RISO+ between the positive terminal of the battery and the ground of the vehicle, while the insulation resistor RISO+ between the positive terminal of the battery and the ground of the vehicle has an infinite resistance value at the time of measuring insulation resistor RISO− between the negative terminal of the battery and the ground of the vehicle. Therefore, there is a problem in that the ground fault detection circuit according to the related art cannot normally measure the isolation breakdown when the insulation of both of the positive terminal of the battery and the negative terminal are broken, that is, the values of both of the insulation resistor RISO+ between the positive terminal of the battery and the ground of the vehicle and the insulation resistor RISO− between the negative terminal of the battery and the ground of the vehicle are small.
Therefore, a need exists for a development of a circuit capable of determining the isolation breakdown without using the ground fault detection circuit forming the current path by connecting among the positive terminal of the battery, the ground, and the negative terminal of the battery.